The present invention relates to macroporous foams comprising microporous zeolite or zeotype material, and to a method for the preparation thereof by using polymeric templates having a thread or film form or a sponge structure. More particularly, the present invention relates to macroporous foams which are prepared by using polymeric templates having a thread or film form or a sponge structure to crystallize microporous zeolite or zeotype material in a thread or film form or a sponge structure, and to a method for the preparation thereof.
The present invention belongs to the inorganic synthesis of synthesizing molecular sieves including zeolite or zeotype materials. xe2x80x9cZeolitexe2x80x9d is a generic name of crystalline aluminosilicate, which constitutes the pore skeleton of zeolite molecules and bears an anionic charge for each aluminum atom. Cations for offsetting such anion charges are present within the very fine pore space which is regularly formed and has a size of not more than 2 nm and the remaining pore space is filled with water. The 3-dimensional pore structure of the zeolite molecules varies depending on the shape and size of the pore, and the pore diameter is usually corresponding to the size of molecules. Therefore, based on the shape and size of the pore, zeolite has the size selectivity for a molecule entering into the pore, and thus, zeolite is called as a molecular sieve.
In the context of the present invention, since zeolite and zeotype materials have micropores having a size of from a few nanometers to several tens nanometers, they are considered as being xe2x80x9cmicroporousxe2x80x9d.
Microporous zeolite and zeotype materials are widely used in the field of households and various industries as a catalyst, adsorbent, ion exchanger, water-absorbing agent, etc. For examples, zeolite shows diverse chemical and physical properties depending on its chemical composition, structure, pre-treatment method, etc. Especially, zeolite itself has a resistance to high temperature and a modified zeolite in which protons are replaced with other cations represents a strong acidic properties to serve as a strong solid acid, the modified zeolite is widely used as a cracking catalyst of crude oil in the petrochemical industry. In addition, such acidic zeolite is widely used as acid catalyst in various chemical reactions as well as a ion exchanger, water-absorbing agent, adsorbent, gas-purifying agent, carrier for a purifying catalyst of exhausting gases of internal combustion engines, additives for detergent, soil improving agent, additives for animal feed, etc. Further, an extensive study is now being made on its application as a sensor carrier in which zeolite is shaped in the form of a thin membrane.
Meanwhile, there are many known zeotype molecular sieves wherein a part or all of silicon (Si) and/or aluminum (Al) atoms constituting the structural skeleton of zeolite molecule are replaced with other elements. For example, a porous silicalite-type molecular sieve in which aluminum atoms are completely eliminated, an alpo(AlPO4)-type molecular sieve in which silicon atoms are replaced with phosphorous atoms, and other molecular sieve or zeotype material wherein skeleton metal atoms are partially replaced with various metal atom such as Ti, Mn, Co, Fe, Zn, etc., have been developed and widely used. In recent, many studies are also being made on mesoporous materials (MCM-series silica) of which pore size is up to several tens nanometers.
Such molecular sieves such as zeolite or zeotype materials are prepared by crystallizing the precursor thereof and generally obtained in the form of fine powder with a diameter of less than about 10 micrometers.
When such zeolite or zeotype materials in the form of powder are filled in a container or reactor, it difficult for a liquid or gaseous fluid to flow through the powder since the spaces between the powder particles are too small. Therefore, a very high pressure is required in order to maintain a sufficient flow velocity in the container or reactor filled with molecular sieve powder, which causes problems that much energy is consumed and the cost for the production of the equipment and reactor is increased. There has been proposed various countermeasures in order to avoid such process problems owing to the pressure dropping phenomena.
A most commonly known method is the method of preparing a zeolite-clay composite, wherein zeolite powder is conglomerated by using clay as a binder to form a paste, which is then granulated to granules with a size of several millimeters, or is extruded in the form of noodle and then cut in a short length [Breck, D. W. Zeolite Molecular Sieves 725-755 (John Wiley and Sons, New York, 1974)]. However, the above-described method requires a mixing step of mixing zeolite with clay, a shaping step, and subsequent treating steps, which causes problems that the overall procedures are troublesome and overall cost for the production is increased. Further, since clay itself is considered as an impurity, the purity of zeolite in the composite is decreased, which causes a decrease of the zeolite using efficiency. Since pores may be blocked by clay particles, the zeolite using efficiency will be rapidly decreased.
In addition, as to granules or extrudates having a size of more than several micrometers, only the zeolite molecules present in the surface of a granule or extrudate generally participate in a reaction since reactants cannot easily access or penetrate into the inner portion of the granules or extrudates. Therefore, if zeolite is conglomerated by mixing with clay, the zeolite using efficiency will be greatly decreased. In addition, as to granules having a size of more than several micrometers, uniform reactivity at a uniform reaction temperature cannot be obtained since there is a temperature difference between the surface and the inner portion of a granule when a reaction is proceeded.
Another widely known technology is the method of coating zeolite film on a support having macropores of millimeters size, wherein the support is made of aluminum, alumina, stainless steel or the like in the form of honeybee or the like in order to facilitate the spread of molecules and various zeolite is coated thereon in the form of a thin film [Bein, T. Chem. Mater. 1996, 8, 1636-1653; Caro, J., Noack, M., Klsch, P. and Schfer, R. Microporous and Mesoporous Materials 2000, 38, 3-24; Clet, G., Jansen, J. C. and van Bekkum, H. Chem. Mater. 1999, 11, 1696-1702; Boudreau, L. C., Kuck, J. A. and Tsapatsis, M. J. Membr. Sci. 1999, 152, 41-59; van der Puil, N., Dautzenberg, F. M., van Bekkum, H. and Jansen, J. C. Microporous and Mesoporous Materials 1999, 27, 95-106; Kormarneni, S., Katsuki, H. and Furuta, S. J. Mater. Chem. 1998, 8, 2327-2329].
The zeolite-support composite particles thus prepared have advantages that the spread of reactants and products and the thermal transfer in all directions are easy, and the temperature distribution is uniform, etc., whereas the efficiency of zeolite used per unit weight are very small since the amount of zeolite used is much less than that of the support. In addition, since the thermal expansion coefficient of the zeolite is different from that of the support, repeated heating of said composite during the process may cause the deprival of the zeolite particles from the support. Further, since the amount of zeolite coated on the support is much less than that of the zeolite precipitated on the bottom of the reaction vessel during the coating process, there is severe waste of zeolite synthetic gel.
Sterte et al. describe a technology to form macropores in a zeolite mass wherein spherical ion exchange resin and active carbon are used as a support and said support is dipped in a synthetic gel to form zeolite thereon by a secondary crystal growing method and then removed by burning [Tosheva, L., Valtchev, V. and Sterte, J. Microporous and Mesoporous Materials 2000, 35-36, 621-629; Valtchev, V., Schoeman, B. J., Hedlund, J. Mintova, S. and Sterte, J. Zeolites 1996,17, 408-415]. However, since the ion exchange resin used as support is more expensive than zeolite and the zeolite mass has only a size of several hundreds micrometer, there is still caused a pressure depression phenomenon in a real application.
Anderson et al. report a direct converting method of porous diatomaceous earth diatom to zeolite by hydrothermal method [Anderson, M. W., Holmes, S. M., Hanif, N., and Cundy, C. S. Angew. Chem. Int. Ed. 2000, 39, 2707-2710]. In such case, there is an advantage that molecules can easily enter and leave via the macropores that the diatomaceous earth possesses by nature. However, since the particle size of the diatomaceous earth itself is basically small, for example of several tens xcexcm, a second shaping step using a binding agent such as clay, etc. should also be needed in order to utilize them.
Stein et al. report a technology wherein polystyrene beads having a uniform size of about 100 micron are compactly charged, amorphous silica is charged and formed in the void space of said beads, and then said amorphous silica is converted to silicalite-1 which is one of zeotype materials, by a secondary method [Holland, B. T., Abrams, L. and Stein, A. J. Am. Chem. Soc. 1999, 121, 4308-4309]. This technology can afford a silicalite-1 in which macropores are distributed, but the overall process is complicated and has a limitation that it cannot be applied for the preparation of zeolite mass comprising both of aluminum atom and silicon atom. Further, a practical use of this technology is difficult in view of economics since the polystyrene beads used are expensive.
Under such circumstances described above, technical problems to be solved in the present invention are as follows:
1) In the foam mass formed with zeolite or zeotype materials, macropores through which molecules can freely spread should be spatially communicated with each other and uniformly distributed all over the foam mass.
(2) The size and shape of macropores formed in a foam should be adjusted in a free and unrestricted manner.
(3) The 3-dimensional outer size and outer shape of a foam comprising zeolite or zeotype materials should be adjusted in a free and unrestricted manner.
(4) The thickness and shape of the layer comprising microporous zeolite or zeotype materials which surrounds the macropores should be easily adjusted, and therefore, the mechanical strength of the foam should be controlled.
(5) Template should be inexpensive, diverse, and easily available.
(6) Preparation processes should be simple.
(7) Processing time should not be long.
(8) There should be reproducibility.
(9) Zeolite and zeotype materials of the foam thus prepared should have a high purity.
(10) Mass production should be allowed.
The present inventors have found that, if a solution, sol or gel of a precursor of zeolite or zeotype materials are charged in a polymeric template having a sponge structure and aged under alkali or acidic condition to crystallize the zeolite or zeotype materials, it is possible to obtain a foam comprising zeolite or zeotype materials and having a sponge structure which is nearly completely resembled to that of the template used, with solving most of or all of said technical problems to be solved as described above.
By using the method proposed in the present invention, it is possible to prepare a foam comprising zeolite or zeotype materials in which macropores (pores having a size of 100 nanometers) are organically linked with each other and have a size of several hundreds micrometers, and therefore, the pressure depressing phenomenon disappears since molecules can move through the macropores present in the foam.
In addition, since it is possible to freely shape template and thus form a zeolite foam having a desired outer shape, a separate shaping step in which clay is used to shape zeolite in a specific form is not needed and thus the cost for the production is remarkably decreased. Further, since there is no blocking problem owing to a binding agent, molecules can freely move inside the zeolite foam having various outer shapes and thus the zeolite using efficiency is substantially increased to nearly 100%.
In addition, since zeolite is formed in the form of a thin layer in the foam even without any separate support, the zeolite using efficiency is further improved. And since molecules can freely enter and leave the nanopores via the macropores, the thermal transfer into the inside of the foam is easy and a uniform reactivity owing to a uniform temperature distribution may be expected.
According to the present invention, therefore, both of the problems of the prior art caused by too small size of synthetic zeolite particles and the problems encountered in the macroporous granule or extrudate which is proposed to solve the problems of the prior art caused by too small size of synthetic zeolite particles can be solved and the object to maximize the zeolite using efficiency can be achieved.
The first object of the present invention is to provide a foam which is prepared by using a polymeric template capable of releasing an amine to crystallize zeolite or zeotype materials in the inner structure and outer shape the same with or similar to those of said template.
According to the concept and theory, it is possible to prepare an article comprising zeolite or zeotype material that is fitted to the inner and outer structure of a polymeric template capable of releasing an amine. Therefore, a variant wherein a polymeric template having a film form is used to prepare an article of film form does not deviate the scope of the present invention.
Therefore, according to one preferred embodiment of the present invention, a polymeric template capable of releasing an amine has a sponge or macroporous structure. In such case, thus prepared foams comprising zeolite or zeotype material has a sponge structure the same with or similar to that of said template.
According to another preferred embodiment of the present invention, a polymeric template capable of releasing an amine has a form of 3-dimension, film, thread or woven fabrics.
In the context of the present invention, the term xe2x80x9csponge structurexe2x80x9d can be understood to illustrate the macroporosity of the polymeric templates. If a part or all of the macropores or bigger inner spaces than said macropores are spatially communicated with each other, it can be expressed as having a sponge structure.
The second object of the present invention is to provide a method for the preparation of a foam, wherein a polymeric template capable of releasing an amine is used to crystallize zeolite or zeotype materials in the inner structure and outer shape which are the same with or similar to those of said template.
As described above, a polymeric template capable of releasing an amine has a sponge or macroporous structure, and has a form of 3-dimensional mass, film, thread or woven fabric.
According to one preferred embodiment of the method of the preparation of the present invention, it comprises dipping a polymeric template capable of releasing an amine group in an alkaline or acidic condition, into a sol or gel containing a precursor of a zeolite or zeotype material, and aging the resultant at a suitable temperature for a period such that the polymeric template can be completely or nearly completely replaced with the zeolite or zeotype materials.